The present invention relates generally to a heat absorbing device and, more particularly, to a heat absorbing element or plate useful in solar collectors.
This invention is especially concerned with heat absorbing elements of the tube-and-fin type where solar radiation incident on the fins is converted into heat energy and conducted by the fins to a tube or tubes containing a suitable heat transfer fluid. To withstand operating fluid pressure and temperature conditions, and to meet various code requirements, the wall thickness of the tube(s) must be rather generous (e.g., 0.020"). The thickness of the fins, on the other hand, need not be as great (e.g., 0.005").
Heretofore, heat absorbing elements of the tube-and-fin type have been produced in many ways, such as by extrusion. In this process, however, the fins and tubes are typically extruded to the same thickness, that is, to the thickness required for the tube walls. Thus the fins are excessively thick and an unnecessary amount of material (e.g., aluminum) is consumed which results in higher manufacturing costs. Absorbers have also been made by bonding tubes (e.g., copper or aluminum tubes) directly to metal sheets (e.g., aluminum sheets). In this process, the thicknesses of the tube walls and fins can be controlled, but bonding the tubes to the sheets raises other problems.
Reference may be made to U.S. Pat. Nos. 4,237,971, 4,227,511 and 4,011,856 for a description of various solar heating devices generally in the field of this invention.